Transmyocardial revascularization (TMR), including endocardial revascularization (ECR), is a surgical treatment for cardiovascular disease. Present ECR procedure is an open chest technique which uses a laser beam to drill holes in the myocardium, specifically a chamber of the heart, typically the left ventricle. These holes or channels extend through the entire heart wall thickness from the outside through to the ventricle. The channels heal on the outside surface of the heart due to external pressure from the surgeon, but remain open on the inside, allowing blood to enter the heart wall tissue from the ventricle.
In another approach ECR could be performed percutaneously using a catheter introduced percutaneously so that the tip of the catheter is inside a chamber of the heart, typically the left ventricle, where the holes or channels can be created from the inside toward but not through the outside of the heart. The energy used to drill these channels can be mechanical, e.g., a needle; electrical, e.g., bipolar or unipolar electric current, r.f., microwave; or optical, e.g., laser. In one combined optical and mechanical approach a holmium laser initiates the channel and a force is applied through the tip of the catheter to deepen the channel. Typically a holmium (HO:YAG) laser or an excimer laser would be used percutaneously. One problem in percutaneous ECR is that, unlike in open chest TMR, channels being drilled are not plainly visible but their depth must be controlled to prevent the channel going all the way through the myocardium and penetrating the outer wall of the heart. Monitoring of the depth can be done with biplanar fluoroscopy but this is expensive and can be confusing even to experienced physicians under the stress of performing heart surgery. This approach is not very reliable; is expensive; requires additional equipment in the operating theater. In another approach the cumulative amount of energy consumed during a drilling is monitored and the drilling is stopped when a certain amount of energy has been expended. This assumes a correlation between hole depth and applied ablative energy and also assumes a thickness of the heart wall, both of which are approximations at best and cannot be relied on for accurate depth gauging. This is a particularly serious problem that needs accurate gauging because if the channel punches through the outer wall of the heart the patient could bleed to death or die of cardiac tamponade if the pericardium is not open due to previous surgery, for example. That would require emergency action to open the chest and stanch the bleeding. This technique, using delivered energy to estimate channel depth, is not reliably accurate nor consistent.